client/src/app/shared/video/infinite-scroller.directive.ts

   1 import { distinct, distinctUntilChanged, filter, map, share, startWith, throttleTime } from 'rxjs/operators'
   2 import { Directive, EventEmitter, Input, OnDestroy, OnInit, Output } from '@angular/core'
   3 import { fromEvent, Subscription } from 'rxjs'
   4
   5 @Directive({
   6   selector: '[myInfiniteScroller]'
   7 })
   8 export class InfiniteScrollerDirective implements OnInit, OnDestroy {
   9   @Input() containerHeight: number
  10   @Input() pageHeight: number
  11   @Input() firstLoadedPage = 1
  12   @Input() percentLimit = 70
  13   @Input() autoInit = false
  14   @Input() container = document.body
  15
  16   @Output() nearOfBottom = new EventEmitter<void>()
  17   @Output() nearOfTop = new EventEmitter<void>()
  18   @Output() pageChanged = new EventEmitter<number>()
  19
  20   private decimalLimit = 0
  21   private lastCurrentBottom = -1
  22   private lastCurrentTop = 0
  23   private scrollDownSub: Subscription
  24   private scrollUpSub: Subscription
  25   private pageChangeSub: Subscription
  26   private middleScreen: number
  27
  28   constructor () {
  29     this.decimalLimit = this.percentLimit / 100
  30   }
  31
  32   ngOnInit () {
  33     if (this.autoInit === true) return this.initialize()
  34   }
  35
  36   ngOnDestroy () {
  37     if (this.scrollDownSub) this.scrollDownSub.unsubscribe()
  38     if (this.scrollUpSub) this.scrollUpSub.unsubscribe()
  39     if (this.pageChangeSub) this.pageChangeSub.unsubscribe()
  40   }
  41
  42   initialize () {
  43     this.middleScreen = window.innerHeight / 2
  44
  45     // Emit the last value
  46     const throttleOptions = { leading: true, trailing: true }
  47
  48     const scrollObservable = fromEvent(window, 'scroll')
  49       .pipe(
  50         startWith(null),
  51         throttleTime(200, undefined, throttleOptions),
  52         map(() => ({ current: window.scrollY, maximumScroll: this.container.clientHeight - window.innerHeight })),
  53         distinctUntilChanged((o1, o2) => o1.current === o2.current),
  54         share()
  55       )
  56
  57     // Scroll Down
  58     this.scrollDownSub = scrollObservable
  59       .pipe(
  60         // Check we scroll down
  61         filter(({ current }) => {
  62           const res = this.lastCurrentBottom < current
  63
  64           this.lastCurrentBottom = current
  65           return res
  66         }),
  67         filter(({ current, maximumScroll }) => maximumScroll <= 0 || (current / maximumScroll) > this.decimalLimit)
  68       )
  69       .subscribe(() => this.nearOfBottom.emit())
  70
  71     // Scroll up
  72     this.scrollUpSub = scrollObservable
  73       .pipe(
  74         // Check we scroll up
  75         filter(({ current }) => {
  76           const res = this.lastCurrentTop > current
  77
  78           this.lastCurrentTop = current
  79           return res
  80         }),
  81         filter(({ current, maximumScroll }) => {
  82           return current !== 0 && (1 - (current / maximumScroll)) > this.decimalLimit
  83         })
  84       )
  85       .subscribe(() => this.nearOfTop.emit())
  86
  87     // Page change
  88     this.pageChangeSub = scrollObservable
  89       .pipe(
  90         distinct(),
  91         map(({ current }) => this.calculateCurrentPage(current)),
  92         distinctUntilChanged()
  93       )
  94       .subscribe(res => this.pageChanged.emit(res))
  95   }
  96
  97   private calculateCurrentPage (current: number) {
  98     const scrollY = current + this.middleScreen
  99
 100     const page = Math.max(1, Math.ceil(scrollY / this.pageHeight))
 101
 102     // Offset page
 103     return page + (this.firstLoadedPage - 1)
 104   }
 105 }